Even when these and other emotions
or sensations are aroused in a very feeble manner, there will
still be a tendency to similar actions, owing to the force
of long-associated habit; and those actions which are least
under voluntary control will generally be longest retained.
Our second principle of antithesis has likewise occasionally
come into play.

Finally, so many expressive movements can be explained, as I trust
will be seen in the course of this volume, through the three
principles which have now been discussed, that we may hope hereafter
to see all thus explained, or by closely analogous principles.
It is, however, often impossible to decide how much weight ought
to be attributed, in each particular case, to one of our principles,
and how much to another; and very many points in the theory
of Expression remain inexplicable. CHAPTER IV.

MEANS OF EXPRESSION IN ANIMALS.

The emission of Sounds--Vocal sounds--Sounds otherwise produced--
Erection of the dermal appendages, hairs, feathers, &c., under
the emotions of anger and terror--The drawing back of the ears
as a preparation for fighting, and as an expression of anger--
Erection of the ears and raising the head, a sign of attention.

IN this and the following chapter I will describe, but only in
sufficient detail to illustrate my subject, the expressive movements,
under different states of the mind, of some few well-known animals.
But before considering them in due succession, it will save much
useless repetition to discuss certain means of expression common
to most of them.

_The emission of Sounds_.--With many kinds of animals, man included, the vocal
organs are efficient in the highest degree as a means of expression.
We have seen, in the last chapter, that when the sensorium is strongly
excited, the muscles of the body are generally thrown into violent action;
and as a consequence, loud sounds are uttered, however silent
the animal may generally be, and although the sounds may be of no use.
Hares and rabbits for instance, never, I believe, use their vocal
organs except in the extremity of suffering; as, when a wounded hare
is killed by the sportsman, or when a young rabbit is caught by a stoat.
Cattle and horses suffer great pain in silence; but when this is excessive,
and especially when associated with terror, they utter fearful sounds.
I have often recognized, from a distance on the Pampas, the agonized
death-bellow of the cattle, when caught by the lasso and hamstrung.
It is said that horses, when attacked by wolves, utter loud and peculiar
screams of distress.

Involuntary and purposeless contractions of the muscles of the chest
and glottis, excited in the above manner, may have first given rise
to the emission of vocal sounds. But the voice is now largely used
by many animals for various purposes; and habit seems to have played
an important part in its employment under other circumstances.
Naturalists have remarked, I believe with truth, that social animals,
from habitually using their vocal organs as a means of intercommunication,
use them on other occasions much more freely than other animals.
But there are marked exceptions to this rule, for instance, with the rabbit.
The principle, also, of association, which is so widely extended in its power,
has likewise played its part. Hence it follows that the voice, from having
been habitually employed as a serviceable aid under certain conditions,
inducing pleasure, pain, rage, &c,, is commonly used whenever the same
sensations or emotions are excited, under quite different conditions,
or in a lesser degree.

The sexes of many animals incessantly call for each other during
the breeding-season; and in not a few cases, the male endeavours
thus to charm or excite the female. This, indeed, seems to have
been the primeval use and means of development of the voice,
as I have attempted to show in my `Descent of Man.' Thus the use
of the vocal organs will have become associated with the anticipation
of the strongest pleasure which animals are capable of feeling.
Animals which live in society often call to each other when separated,
and evidently feel much joy at meeting; as we see with a horse,
on the return of his companion, for whom he has been neighing.
The mother calls incessantly for her lost young ones; for instance,
a cow for her calf; and the young of many animals call for their mothers.
When a flock of sheep is scattered, the ewes bleat incessantly for
their lambs, and their mutual pleasure at coming together is manifest.
Woe betide the man who meddles with the young of the larger and
fiercer quadrupeds, if they hear the cry of distress from their young.
Rage leads to the violent exertion of all the muscles, including those
of the voice; and some animals, when enraged, endeavour to strike
terror into their enemies by its power and harshness, as the lion
does by roaring, and the dog by growling.